In previous chapters we have discussed most of the basic ingredients required for the design of an infrared system. In the remaining chapters we attempt to bring these basic technologies together and apply them to the design of several system concepts. Initially we introduce the concepts of staring and scanning sensors, followed by examples of modern thermal imaging systems using both staring and scanning techniques. We then discuss several signal processing techniques for extracting a target signal from a cluttered background. Finally, we describe and analyze several system concepts covering a wide variety of surveillance applications. However, before doing so, we set the stage by developing the basic range equation and present various forms that have been used by system engineers for both staring and scanning systems.